An obvious intent of any automatic recovery system for almost any aircraft is to prevent ground impact during controlled flight of the aircraft. Many aircraft have standard proximity alarms for alerting pilots to the nearness of ground. These alarms can be based on inadmissible rates of descent of the aircraft or nearness of the ground. While proximity alarms are an improvement over prior systems, they are not a permanent solution to some of the problems that have been shown to cause aircraft ground impacts.
The need for ground collision avoidance extends to a wide variety of aircraft and scenarios ranging from terminal area navigation for commercial airliners to low level navigation, pilot spatial disorientation and g-induced loss of consciousness (G-LOC) for high performance aircraft. While some aircraft have been equipped with ground proximity warning systems, most of the existing ground proximity warning systems contain no provisions for variations in aerodynamics, but rather rely on the pilot to compensate for these variations by giving him a finite amount of time to recover level flight. At the same time, these systems are passive, relying on pilot awareness and competence to recover from the situation.
An innovative approach to this problem is disclosed in U.S. Pat. No. 4,058,710 to Altman. Altman discloses a process for preventing unwanted contact by an aircraft with land or water. When applied over land Altman assumes flat terrain or low hills. Altman's process utilizes the aircraft's rate of descent and altitude to compute a limiting altitude, which is further modified by the aircraft's ability for transverse acceleration. This limiting altitude is used to determine when to activate an automatic feedback controller, which provides the aircraft with the maximum feasible transverse acceleration. Thus, Altman attempts to continuously calculate a limiting altitude for the aircraft below which automatic controls will be applied for aircraft recovery. Various theoretical schemes are proposed by Altman for determining this limiting altitude. All of these schemes are difficult to incorporate into an aircraft control design or to simplify in a manner that will not cause spurious effects including nuisance flyups during controlled flight.
The current Enhanced Ground Proximity Warning System (EGPWS) is designed to provide pilots with timely alerts in the event that the airplane is flown towards terrain or an obstacle. The EGPWS alerting algorithms are predicated on the expectation that the response of the pilot to a warning will be a “pull-up”, i.e. a maneuver in the vertical plane only. If an aircraft is about to enter restricted airspace, it may not be possible to avoid the airspace by using a “pull-up” maneuver alone. Also, some airspace volumes expand laterally with altitude, and again a “pull-up” may not avoid penetrating the airspace volume.
A need therefore exists for a ground, obstacle, and protected airspace auto-recovery system that is sufficiently sophisticated to initiate a recovery maneuver when required while avoiding a multitude of nuisance recoveries that interfere with controlled flight and providing smooth recovery maneuvers for crew and passenger safety and comfort.